Use unittest.mock instead of third party mock

Now that we no longer support py27, we can use the standard library
unittest.mock module instead of the third party mock lib.

Change-Id: I435d32bf034040325128f2b5275d907062d63351
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

congressclient/tests/common.py

@@ -12,8 +12,8 @@
 #
 
 import argparse
+from unittest import mock
 
-import mock
 
 from congressclient.tests import utils
 

congressclient/tests/v1/test_api_versions.py

@@ -13,7 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
 
 from congressclient.osc.v1 import api_versions
 from congressclient.tests import common

congressclient/tests/v1/test_datasource.py

@@ -11,7 +11,8 @@
 #   under the License.
 #
 
-import mock
+from unittest import mock
+
 from oslo_serialization import jsonutils
 
 from congressclient.common import utils

congressclient/tests/v1/test_drivers.py

@@ -11,7 +11,7 @@
 #   under the License.
 #
 
-import mock
+from unittest import mock
 
 from congressclient.osc.v1 import driver
 from congressclient.tests import common

congressclient/tests/v1/test_policy.py

@@ -11,8 +11,8 @@
 #   under the License.
 #
 import os
+from unittest import mock
 
-import mock
 
 from congressclient.common import utils
 from congressclient.osc.v1 import policy

test-requirements.txt

@@ -7,4 +7,3 @@ coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
 stestr>=2.0.0 # Apache-2.0
 testtools>=2.2.0 # MIT
-mock>=2.0.0 # BSD